Use of a catalyst employing molybdenum, phosphorus, arsenic, copper and ammonium is shown in West German Provisional Pat. No. 2,353,131. Catalysts containing oxides of molybdenum, arsenic, phosphorus and optionally cobalt, aluminum or copper on a support having external macropores are disclosed in U.S. Pat. No. 3,761,516.
Unexpectedly higher yields and selectivities of acrylic acid and methacrylic acid are obtained using the coated catalysts of the invention.